1. Technical Field
The present invention relates in general to portable electronic devices and, in particular, to providing location and other information to portable electronic devices such as personal digital assistants (PDAs), palmtop computers, cameras, etc. Still more particularly, the present invention relates to a method and system for providing location and other information to portable electronic devices lacking global positioning system (GPS) reception capability.
2. Description of the Related Art
A global positioning system (GPS) has been utilized since the early 1980""s to provide position and time information to earth-based GPS receivers. GPS includes a large number of earth-orbiting satellites that each transmit a signal containing information that permits distance measurement to be made by measuring the transit time of a pseudo-random number (PRN) code from the satellite to a GPS receiver. The GPS receiver decodes a received signal by sampling the PRN code and correlating the samples with a replica code generated by the GPS receiver, thus permitting the GPS receiver to distinguish between the GPS signal and the earth""s background noise. The PRN code typically includes an implicit time signal, as measured by an atomic clock on board the GPS satellite, at which the signal left the satellite. Over time, the signal transmitted by a satellite also includes information regarding the satellite""s current orbit as well as corrections for known errors in the satellite""s clock. Utilizing signals received from multiple satellites, a GPS receiver can obtain relatively accurate information regarding its current position and the current time.
While GPS receivers are becoming increasingly popular in both military and consumer applications, it is currently cost prohibitive to incorporate a GPS receiver into every portable electronic device for which position and time information could be useful. As should thus be apparent, it would be useful and desirable to provide position and other information to a portable electronic device lacking GPS reception capability.
In accordance with the present invention, a portable electronic device that can obtain position information despite lacking GPS reception capability includes data storage that stores a reference position, a plurality of inertial motion sensors, and computational circuitry. The inertial motion sensors detect movement of the portable electronic device and output motion signals to the computation circuitry indicative of the sensed movement. In response to these motion signals and the stored reference position, the computational circuitry computes a position of the portable electronic device.
All objects, features, and advantages of the present invention will become apparent in the following detailed written description.